Two people were injured in the first drone hit on a residential building outside Ukraine since the start of Russia's full-scale invasion in 2022.

Romania called the incident a "serious and irresponsible escalation" by its neighbour and expelled a Russian diplomat in a first response.

But Putin said Russia "has never threatened and is not threatening European countries".

"No one can say the origin of this or that aircraft until an examination of that aircraft is conducted," he said during a visit to Kazakhstan.

"If they provide us with any objective data... in that case, we will assess what happened."

Romania's Defence Minister Radu-Dinel Miruta told a press conference that the serial numbers on the missile showed it was "undoubtedly" Russian.

Here is what we know about the drone crash:

- What happened? -

The drone hit the roof of an apartment building in the centre of the city of Galati, close to the border with Ukraine. It set off a fire and a 14-year-old boy and 53-year-old woman were taken to hospital, officials said.

Dozens of drones have drifted into Romania since the start of the Ukraine war, but no residential buildings had previously been hit.

The Romanian defence ministry said two F-16 fighter jets were scrambled in response to the drone, which it said entered Romania's airspace during Russian strikes on Ukraine.

- Why wasn't the drone stopped? -

Romanian forces had insufficient time -- four minutes -- to shoot down the drone, General Gheorghe Maxim from the Joint Forces Command said. There were "no realistic opportunities to engage it safely", he added.

A senior NATO military official said: "NATO detected and tracked the Russian drone, but it entered Romanian airspace only minutes before striking the apartment building in Galati."

The official said the drone was moving at nearly 200 kilometres (125 miles) an hour and Galati was less than 15 km (nine miles) from the border.

- How has Romania responded? -

Romania summoned the Russian ambassador, and President Nicusor Dan convened a national defence council meeting on "the most serious incident to have affected our national territory" since Russia invaded Ukraine.

Dan said Romania would expel the Russian consul general in the city of Constanta and close the mission. Russia said it was preparing "retaliatory measures".

The Russian embassy said no proof had been given that the drone was Russian. Romania's Defence Minister Radu-Dinel Miruta invited Russian officials to inspect the drone debris.

"Based on the serial numbers of the components found there, this is undoubtedly a Russian-made product," he said.

Dan said that in a conversation, NATO chief Mark Rutte had promised help to get air defence equipment "as quickly as possible". Ukraine's President Volodymyr Zelensky has also promised help.

Inhabitants of Galati questioned why there were not anti-drone systems in the city so close to the frontier.

Dan -- whose country faces political turmoil after the prime minister was ousted in a no-confidence vote this month -- was booed when he visited the site of the crash, with some chanting "resignation".

- What have the EU and its allies said? -

EU chief Ursula von der Leyen said Russia's "war of aggression" had "crossed yet another line", pledging to increase deterrence on the EU's eastern border.

German Chancellor Friedrich Merz said the incident showed Russia's "willingness to escalate", and Britain's Keir Starmer condemned the "serious violation of NATO airspace".

France said it had summoned the Russian ambassador. Britain's Prime Minister Keir Starmer condemned what he called a "serious violation of NATO airspace".

The US ambassador to NATO, Matthew Whitaker, also slammed the "reckless incursion", saying: "We stand with our NATO ally."

- What will NATO do next? -

"Russia's reckless behaviour is a danger to us all," NATO chief Rutte wrote on social media.

"NATO stands ready to defend every inch of Allied territory."

NATO sources said there was no indication whether Romania would call for emergency consultations.

Such consultations have been called three times during Russia's full-scale war on Ukraine: the first just after the invasion in 2022, once by Poland after incursions by Russian drones, and once by Estonia after Russian fighter jets violated its airspace.

burs-tw/pdw